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HARRY HAMMOND HESS
HARRY HAMMOND HESS
Answers!!
- 1962
- 1.5 km
- the centre
by Joe Langan
but...
His theory today
In 1963, Fred Vine and Drummond Matthews at Cambridge University proposed a corollary to Hess's hypothesis. 'If the seafloor is created at the mid ocean ridges and spreads outward and if the earth's magnetic field reverses polarity every few thousands of years then the seafloor should be made of magnetized strips running parallel to the mid ocean ridges, alternating between normal and reverse polarity.' Their idea, proposed independently by Lawrence Morley of the Geological Survey of Canada, was confirmed a few years later when scientists found the underwater bands of differently magnetized rocks. This theory more or less backed up Hess's theory but went into further detail.
improved seismic data confirmed that oceanic crust was indeed sinking into the trenches, fully proving Hess' hypothesis, which was based largely on intuitive geologic reasoning. His basic idea of seafloor spreading along mid-oceanic ridges has well withstood the test of time.
The theory
Hess thought that oceans grew from their centers, with molten material oozing up from the Earth’s mantle along the mid ocean ridges. This created new seafloor which then spread away from the ridge in both directions. The ocean ridge was thermally expanded which made it higher than the ocean floor further away. As spreading continued, the older ocean floor cooled and subsided to the level of the abyssal plain which is about 4 km deep.
QUIZ QUESTIONS!!!!!!!!
- When was the theory made public?
- How high do the mid ocean ridges usually rise above the sea floor?
- Where did Hess think that oceans grew from?
what did Hess find out?
Hess discovered that the oceans were shallower in the middle. He also identified the presence of Mid Ocean Ridges which raised above the surrounding generally sea floor, which was usually flat, by as much as 1.5 km. Also he found that the deepest parts of the oceans were very close to continental margins in the Pacific with Ocean Trenches extending down over 11 km.
Who was he?
Harry Hess was a professor of geology at Princeton University in the USA.
He became interested in the geology of the oceans while serving in the Navy in World War II. His time as a Navy officer was an opportunity to use sonar, then a new technology, to map the ocean floor across the North Pacific ocean.